1. Field of the Invention
The present invention relates to an apparatus and method for generating and sensing torsional vibrations, which can perform torsional modal testing of a structure including shafts, beams and pipes, and more particularly, to an apparatus and method for generating and sensing torsional vibrations using magnetostriction, which can perform modal testing of a structure by subjecting a part to be tested to torsional vibrations using a magnetostrictive phenomenon and simultaneously sensing the torsional vibrations.
2. Description of the Related Art
When machines having parts such as pipes, beams, bars, shafts, or the like are designed, modal testing should be performed in order to assure the structural stability of the machine parts in various operational cases. Through a modal testing, we can measure the dynamic characteristics of a machine part including natural frequencies and mode shapes. For example, if the machine part is operating at the vibration frequency similar to its natural frequency, the machine part can be broken due to resonance. If we consider the natural frequency of the machine part during the process of the machine and machine element design, we can prevent the fracture due to their resonance. Therefore, it is preferable to performing the modal testing of machine parts during the process of the machine and machine element design.
Modal testing for grasping the dynamic characteristics of members such as pipes, beams, bars, shafts, or the like about torsional vibrations is performed by subjecting a part to be tested to torsional vibrations and measuring the response of the part. Therefore, there is a strong demand for an apparatus and method capable of generating torsional vibrations for testing a part and sensing the torsional vibrations of the part.
As used herein, magnetostriction or Joule effect denotes a phenomenon where a mechanical deformation of a part made of a ferromagnetic material and placed in a magnetic field is generated. On the other hand, inverse magnetostriction or Villari effect denotes a change of a magnetic state of a part when a stress is applied to the part.
Accordingly, the deformation of a part to be tested can be measured without mechanically contacting the part using magnetostriction. For this reason, magnetostriction has been widely applied in various fields where a contact sensor or an actuator cannot be employed.